Glass fibers are typically formed from either "621" or "E" glass compositions.
"621" GLASS HAS A COMPOSITION OF:
______________________________________ Component Percent by Weight ______________________________________ SiO.sub.2 52-56 Al.sub.2 O.sub.3 12-16 CaO 19-25 B.sub.2 O.sub.3 8-13 ______________________________________
as disclosed in U.S. Patent No. 2,571,074. This glass also includes such impurities as Fe.sub.2 O.sub.3, SrO, K.sub.2 O, Na.sub.2 O, Li.sub.2 O. The glass additionally may contain CaF.sub.2.
"E" glass has a composition of:
______________________________________ Component Percent by Weight ______________________________________ SiO.sub.2 52-56 Al.sub.2 O.sub.3 12-16 MgO 3-6 CaO 16-19 B.sub.2 O.sub.3 9-11 ______________________________________
and includes the same impurities as the "621" glass. In these compositions, fluorine is added to the batch to be melted into glass as CaF.sub.2. The amount of fluorine in the glass batch often approaches 2 percent by weight or more. As the glass is melted, much of the fluorine in the batch materials is volatilized and driven off as a fluorine containing gas in the stack. Fluorine containing gases are highly corrosive materials and are known sources of pollution. Further, the fluorine component of the glass acts to raise the liquidus temperature of the glass.
However, CaF.sub.2 acts as a flux in melting the glass, and helps reduce the softening point temperature of glass compositions. Control of liquidus and softening point temperatures is vital in the formation of glass filaments, as these factors, as is well known in the art, help determine the temperatures at which the glass fiber forming operation must be carried out. As these temperatures rise, the temperatures of operation must also rise, thus resulting in added fuel costs and shorter life for the furnace, bushing, and other associated equipment. Thus, it is highly desirable to replace the fluorine components of the glass batch, and to replace them with a material which itself will help reduce the softening and the liquidus temperature of the glass composition and thus help reduce fuel consumption, in addition to reducing fluorine pollution.